In many implementations, it is often advantageous to have a power regulator that can use either an external pass device or an internal pass device as part of the general regulator topology. The pass device is that device in a series (as distinct from shunt) regulator that passes current from the power source to the load. Use of an external pass device is generally done to place most of the power dissipation on the external pass device, rather than entirely with the remainder of the regulator, which may be on an integrated circuit (IC). The integrated circuit may or may not have other significant power dissipation sources, so thermal management may be a system concern. An internal pass device is usually selected when power dissipation is not a concern, and the area and cost of the external pass device may be avoided. The topology of a series regulator using a series pass transistor for a pass device whose low impedance terminals couple a source of power to a load and whose high impedance terminal couples to an error amplifier that increases difference between an output, which may or may not be scaled, and a reference signal is known.
However, the known power regulator devices suffer from a lack of stability under differing conditions. Although stability can be easily achieved for an external pass device over the full range of output current using external compensation circuitry, the same compensation network cannot guarantee the stability while using an internal pass device.